1. Technical Field of the Invention
The present invention relates to a radar system that detects the position of a target using a high-resolution algorithm.
2. Related Art
Some types of radar systems are well known. One type of well-known radar system uses array antennas composed of a plurality of antenna elements to detect the distance to a target that has reflected radio waves or the direction of arrival of radio waves (i.e. a direction in which the target is present).
As mentioned in JP-A-2006-047282, so-called high-resolution algorithms, such as MUSIC (Multiple Signal Classification), ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) and the like, are well known as methods of estimating the direction of arrival of radio waves. In a method using such a high-resolution algorithm, an angle spectrum is prepared according to a correlation matrix that shows correlation between signals received by antenna elements (also referred to as “channels”). Then, in the method, the angle spectrum is scanned to estimate the direction of arrival of radio waves.
In a high-resolution algorithm, an angle spectrum is prepared in a process of calculating the direction of arrival of radio waves. Specifically, in preparing an angle spectrum in the process, the number of reflections is estimated so that the estimated number of peaks is formed. Accordingly, if the estimated number of incoming waves is incorrect, unnecessary peaks (noise peaks) may be formed to unnecessarily detect a target that is not actually present (hereinafter this detection is referred to as “unnecessary detection”). An unnecessary detection may cause unnecessary control such as in an ACC (Adaptive Cruise Control) system of a vehicle. Therefore, the unnecessary detections have to be reduced as much as possible.
When a high-resolution algorithm is used, peaks are detected in the calculation with unnecessary fine resolution. Therefore, use of a high-resolution algorithm raises a problem of exposing noise peaks that would have been buried in peaks based on the waves reflected from a target in so-called Beam-former method.
On the other hand, as described in JP-A-2006-047282 as well, several attempts are made to enhance the accuracy of estimating the number of reflections. However, currently, sufficiently satisfactory results are not yet available.